This is the most accurate map I have of where the tunnel actually is.
Those houses "fronting on 15th" don't actually; they have their backs to 15th. Apparently the developer didn't think they'd sell if they fronted on 15th, so he flipped them around and then had to arrange an easement for them to be accessed from the private street to the north. I'll have to go look up whether they're a condo association or have fee ownership. EDIT: They have fee-simple ownership of their lots.